The project is focused on studies of gene expression during development in Drosophila melanogaster. Two projects are being pursued. One involves the characterization of a region of the X chromosome bordered by the white and Notch loci. It is a region containing more than 500 kb of DNA but only four mutant phenotypes have been discovered for the region and all are associated with chromosome breaks. No point mutations have as yet been identified despite extensive mutation screening of the region. The region is rich in repeated nucleotide sequences, which makes cloning and sequencing difficult. One of the phenotypes derives from a small deletion that acts in cis as a dominant suppressor of the zeste-1 mutation. The zeste locus encodes a transcription actor that our results suggest is involved in establishing and maintaining transcriptionally active domains in chromatin. Another developmentally regulated locus being studied is echinus, a gene that plays a role in development of facets in the compound eye. The gene has been cloned and both genomic and cDNA clones have been sequenced. The putative protein product is not similar to any other protein in the data bank. Transformation experiments to rescue mutants are in progress.